Method and apparatus for soil gas analysis



May 26,` 1942.

H. N. HERRICK METHOD AND APPARATUS FOR SOIL GAS ANALYSIS f Filed Jan. 28,A 1939 Ill Henry /V. Herr/'ck I N V E N TO R ATTORN EY Patented May 26, 1942A METHOD AND APPARATUS FOR SOIL GAS ANALYSIS Henry NQHerrlck, Berkeley, Calif., assgnor to Standard 0il Company of California, San Francisco, Calif., a corporation of Delaware Application January 28, 1939, Serial No. 253,375

'z claims.l (ci. ca -257) This invention relates to the location of deposits of hydrocarbon material such as petroleum, natural gas or the like beneath the surface of the ground and particularly refers to an improved method and apparatus for obtaining samples of hydrocarbon gases which diiuse upwardly through the earth at a very slow rate.

Heretofore samples of gases which diffuse upwardly through the soil have been obtained by forming a relatively shallow bore hole in the earth, sealing its upper end from the atmosphere and lowering the pressure therein, as by a vacuum pump, so that gases in the soil surrounding the bore will be drawn rapidly into an absorber for subsequent analysis. These Ainstallations required a continuously operating vacuum pump and only resulted in the accumulation of very small quantities of the desired hydrocarbons in the absorber. Because of the necessity for mechanical equipment connected to each sampling point, the investment in apparatus was high and required continuous attendance and source of power.

It is an object of this invention'to provide a very simple Aand economical method and apparatus for obtaining samples of hydrocarbon gases from the soil which require no attendance or source of power and which will accumulate greater quantities of the desired hydrocarbons in readily recoverable form than those methods f heretofore used.

Another object is to provide a method and apparatus for obtaining samplesof soil gases which may be placed in position and allowed to remain for a relatively long period, accumulating hydrocarbon gases at their natural rate of eiusion and collecting them in a form which is readily susceptible of analysis.

Another object is to provide a method and apparatus for collecting soil gases which utilize variations in the pressure of the atmosphere toy ferred form of collecting apparatus in place in v Figure 2 is a vertical sectional view of an alternative form of an apparatus suitable for practicing this method.

In the drawing, reference numeral II) designates the surface of the ground in which is formed a bore hole II which may be 10 to 20 feet indepth. In the embodiment shown in Figure 1, bore hole I I may be made with a step or ledge I2 to receive "a flange I3 at the lower end of a casing I4, the latter extending upwardly toa point somewhat above the surface I0 and terminating in a loose cap or cover I5.

Flange I3 is preferably provided with a central opening I6 which is adapted to receive a cork or packing means Il. The sampling tube consists of a length of pipe I8 at the lower end of which is a coupling I9 and a canister or container 20, the latter provided with a screen 2| near its lower end and terminating in a downwardly extending nipple 22, the latter adapted to be received in packing member Il.

Canister 20 is filled with a loosely packed adsorption medium 23 offering substantially no resistance to gas flow, which may be activated carbon, silica gel or other suitable material in which hydrocarbon gases may be collected. The bore holeJI above step I2 is preferably sealed by means of sand or mud 24 which is introduced around casing I 4 and retained on the outer eX- tension of flange I3.

In operation this device is permitted to remain vfor a considerable period, for example several weeks or even months, the normal variations in atmospheric pressure serving to cause passage of soil gases upwardly through adsorption medium 23 whenever a decrease in`-pressure 0ccurs. Increases in atmospheric pressure will obviously force air downwardly through the adsorption medium, but this will have no effect upon it or upon the hydrocarbon gases which may be retained therein. The rate of effusion of hydrocarbon gases from the soil is necessarily very slow but will be found to correspond generally with the -rate of breathing of these gases through the collecting means by the atmospheric pressure variations. These latter include the diurnal variation which will be supplemented by the greater changes due to the passage of storms and the like.

Referring to Figure 2, the apparatus there shown includes a pipe I8 and coupling I9 at the lower end of which is a container 20 fitted with a screen 2| and open at the lower end to the space within bore hole II. The upper end of pipe I8 may be provided with a U-'shaped tting 25 to prevent rain or foreign materials from entering the upper end of the pipe. A packing means 26, which may be a simple wrapping of cloth, a plug of soil or any easily available means, may be used to isolate the lower part of bore hole -II from the atmosphere. Obviously the pressure drop through pipe I8 and adsorption material 23 will be very small under any normal variation in barometric pressure so that there is no necessity for making a particularly gastight seal between the upper end of the bore Il and the atmosphere.

After the adsorption material 23 has been permit-ted to remain in bore hole Il for the desired period, depending upon the amount of gas which may be diffusing upwardly through the soil, it is removed and the hydrocarbon gases driven therefrom by means of steam or other well known procedures and the composition of the gases determined.

This method andA apparatus appear to diier from those previously known by the utilization I of an adsorption medium exposed to gases withdrawn from an isolated portion of a bore hole in the earth by means of natural variations in the atmospheric pressure. Although specic means are shown for practicing this invention it will be understood that many modifications and variations could be made and it is understood that all those which fall within the scope of the appended claims are embraced thereby.

I claim:

1. An apparatus for collecting hydrocarbon gases from a shallow bore in the earth comprising an open-ended conduit adapted to be sealed in a bore hole in the earth, a container connected to said conduit, and adsorption means in said container, said adsorption means arranged to oier substantially low resistance to the passage of gas through said container and said conduit under vthe pressure differentials caused by variations in atmospheric pressure.

2. An apparatus for collecting hydrocarbon gases according to claim 1 in which said adsorbent material comprises activated carbon.

3. An apparatus for collecting hydrocarbon gases according to claim 1 in which said adsorbent material comprises silica gel.

4. An apparatus for collecting hydrocarbon gases according to claim 1 in which said sealing means comprises acasing concentric with said conduit, a closure for the lower end of said casing, a passage through said closure, said conduit adapted to extend through said passage to communicate with the bore hole beneath said closure, and sealing means between the Wall of said passage and said conduit.

5. A method for collecting a sample of gas present in a body of porous material, which comprises substantially sealing an adsorbent material for the gas to be collected between gas in a `space formed in said porous material and another gas at natural atmospheric pressure, said adsorbent material being open to gas in said space and to said other gas, subjecting the portion of said adsorbent material open to said other gas to the natural variations in atmospheric pressure to force a portion of said other gas into said adsorbent material on a rise in the natural atmospheric pressure and to force a portion of said gas within said space into said adsorbent material on a fall in the natural atmosp heric pressure, whereby a portion of the gas within'said space is adsorbed by said adsorbent material.

6. A method of collecting a sample of hydrocarbon gas present in the earth, which comprises substantially sealing an adsorbent material for the hydrocarbon gases to be collected between gas in a` space formed in the earth and the atmosphere, said adsorbent material being open to gas in said space and in communication with the atmosphere, subjecting the portion of said adsorbent material in communication with the atmosphere to the natural variations in atmos- Vpheric pressure to force a portion of the atmosearth by a lower portion of a shallow bore in the earth, said adsorbent material being open to the gas in said space and in communication with the atmosphere, subjecting the portion of said adsorbent material in communication with the atmosphere to the natural variations in atmospheric pressure to force a portion of the atmosphere into said adsorbent material on a rise in the natural atmospheric pressure and to force a portion of said gas within said space into saidy adsorbent material on a fall in the natural atf mospheric pressure, whereby a, portion of the4 hydrocarbon gas within said space is adsorbed by said adsorbent material.

HENRY N. HERRICK. 

